Three-dimensional man-machine interaction

The film accompanied by this paper illustrates an experimental system for real-time Computer-Aided Geometric Design of three-dimensional parametric surfaces. A detailed description of the system is given in another paper by the author(1). Its principle features are that it operates in real-time, all geometric interaction with the surfaces is accomplished with a 3-D Wand, the surfaces are viewed in 3-D using a head-mounted display, and the surfaces are mathematically represented using parametric spline surface patches.The two principle computing components of the system are a PDP-10 computer and an LDS-1 display computer. The PDP-10 acts as a host to the LDS-1. Its main tasks each 1/30 second are to compute the 3-D Wand and head-mounted display positions and to incrementally update the geometries of the surface patches being designed by the user. During the same time period, the LDS-1 loads its digital matrix multiplier with the room-to-head transformation matrix provided to it by the PDP-10, displays on the head-mounted display's CRT's a line drawn rendering of all of the parametric surface patches that are within the 40 degree field-of-view of the display and displays a small cube to represent the current position of the Wand.The user of the system initiates a design sequence by selecting a patch description file from the PDP-10's file system. He then puts on the head-mounted display and uses the 3-D Wand with its control buttons to grasp the patches, which appear to float before him in the room, and make appropriate changes to their geometry. After a design sequence he may save the new surfaces on the PDP-10 file system and select certain views of the surfaces to be rendered as a continuous-tone shaded picture with hidden-surfaces removed.The first part of the film described here shows the system in real-time operation. During this part, several free-form surfaces are manipulated as the camera records the action on a line-drawing monitor. The second part of the film illustrates a continuous-tone, shaded rendering of a design sequence. The continuous-tone rendering was produced "off-line" using pertinent viewpoint information that was saved during the design sequence. The final few minutes of the film depict the construction of a Klein-Bottle.